In hard disk devices for magnetic recording, because the magnetic head contacts the hard disk a lubricant is applied to the surface of the hard disk. Known lubricants of this kind include a perfluoropolyether diol having hydroxyl groups at both ends (Z-DOL, Ausimont), a perfluoropolyether dicarboxylic acid having carboxyl groups at both ends (Z-DIAC, Ausimont), and a perfluoropolyether tetraol having propylene glycol residues at both ends (Z-TETRAOL, Ausimont).
A perfluoropolyether ester derivative has also been proposed wherein a perfluoropolyether residue is bound to a long-chain alkyl group or perfluoroalkyl group via an ester bond (see Japanese Patent Application Laid-open No. H5-194970).
However, because it is expected that the next generation of compact hard disk devices for magnetic recording which allow high-density recording will be mounted in passenger vehicles, in which the indoor temperature is relatively high, they will need to be more heat-resistant, and in particular the lubricant applied to the outer surface of the hard disk will need to be heat-resistant at 300° C. or more.
In the case of the commercial lubricants described above (perfluoropolyether diol, perfluoropolyether dicarboxylic acid, perfluoropolyether tetraol), however, the problem is that the decomposition temperature is about 270° C. at most and the extinction temperature is about 450° C. at most, so the requirement of heat resistance at 300° C. or more is not met. Even in the case of the perfluoropolyether ester compound described in Japanese Patent Application Laid-open No. H5-194970, the decomposition temperature is no more than about 280° C. at most so the requirement of heat resistance at 300° C. or more is not met.
One possible way of improving the heat resistance of these perfluoropolyether derivatives which are lubricants would be to remove from the molecule the functional groups which are starting points for decomposition, but this is not a practical response considering the decrease in adhesion with the hard disk surface. The molecular weight of the perfluoropolyether derivative could also be increased by increasing the number of repeating units thereof, but this would be unlikely to yield a perfluoropolyether derivative with a narrow molecular weight distribution and stable characteristics.
It is an object of the present invention to resolve the aforementioned problems of background art and allow a novel perfluoropolyether derivative which is useful as a lubricant and exhibits a decomposition temperature of 300° C. or more to be provided in an industrially convenient way.